Zhiyong Zhang and colleagues from the Chinese Academy of Sciences' Institute of High Energy Physics exposed larvae of the widely used model organism C. elegans to 8.5-nanometer particles of CeO2. Nanoparticles of CeO2 have many high-tech uses, such as in catalytic converters and as polish for silicon wafers. They are also under consideration for use in eye drops and sunscreen.

Research on other nanoparticles has suggested that they can trigger oxidative stress in C. elegans. But studies on CeO2 nanoparticles have hinted that theymay actually protect against cardiovascular, neurological, and radiological damage in rats, mice, and human cells in vitro, respectively. However, those studies used high concentrations of the nanoparticles. Zhang wanted to see how environmentally relevant concentrations of CeO2 nanoparticles might affect an organism's health.

The researchers raised C. elegans larvae on mats of bacteria doped with CeO2 nanoparticles at concentrations ranging from 1 to 100 nM. They then counted the surviving worms each day.

At the lowest concentration of 1 nM, the mean lifespan of the worms was 15 days. At the highest concentration of 100 nM, the worms lived 14 days. Compared to control worms' lifespan of nearly 18 days, the lifespan of worms exposed to nanoparticles decreased by 12% when averaged over all concentrations. The researchers think the shortened lifespan is related to oxidative stress.

"We never expected to find any negative effects at such a low concentration," Zhang says. This is the first study, he says, indicating adverse effects of nanoparticles in the 1- to 100-nM range.